An image reading apparatus reads an image on a sheet by using an image sensor such as a charge coupled device (CCD) or a contact image sensor (CIS). In such an image reading apparatus, when reading a sheet other than a standard sized sheet such as a name card or a receipt, the sheet is read as any standard size. However, if the non-standard sized sheet is read as a standard size, there is a possibility that the image includes a portion in which there is no sheet.